Versatile workpiece holding system utilizing connectors selectively positional on work table

ABSTRACT

A workpiece holding system includes a connector for mounting a workpiece-holding pallet or upper plate to a workstation with the high degree of accuracy that is necessary for workpiece machining operations. The upper plate connects to the workstation via a pair oppositely directed, extendable/retractable connectors aligned along an axis of connection, with a total of four connectors and two spaced axes of connection, though three such connectors may also be used. At least one of the connectors includes a pin, an actuating knob and a wrap spring, thereby to permit extension and retraction along the respective axis by rotation of the actuating knob. The wrap spring interconnects the actuating knob to the pin in a slippable manner. The wrap spring acts as a torque limiting device during rotation of the knob to extend the pin into engagement with the upper plate, and it acts as a clutch during rotation of the knob to retract the pin from engagement with the pallet. The wrap spring provides advantage in automating work-holding operations. Additional versatility in work-holding operations may be achieved by mounting a plurality of the connectors to a like number of pillars which are selectively positionable to a work table, thereby to hold a workpiece in three dimensional space.

This application is a continuation-in-part of applicant's U.S. patentapplication Ser. No. 07/922,680, filed on Jul. 30, 1992, entitled"Improved Pallet/Sine Plate Connector" now U.S. Pat. No. 5,363,563.

FIELD OF THE INVENTION

This invention relates to a workpiece holding system with increasedversatility in mounting a workpiece-holding pallet, a sine plate or aworkpiece at a desired position above a workstation, or work table.

BACKGROUND OF THE INVENTION

Applicant's co-owned U.S. Pat. No. 4,927,125 discloses a set-up assemblywith upper and lower plates hingedly connectable and disconnectablealong two spaced parallel axes. Applicant expressly incorporates U.S.Pat. No. 4,927,125 by reference herein, in its entirety. Aligned witheach axis, the set-up assembly includes a pair of axially extendable andretractable center pins mounted on one of the plates which may bequickly and easily moved along the axis into and out of engagement withthe other plate. The use of extendable and retractable center pins toaccurately hold the upper plate to the lower plate simplifies set upoperations and reduces the operator's set-up time for those machiningoperations which require hinged raising of either end of the upperplate.

The extendable and retractable center pins also facilitate machiningoperations which require simple, fast and effective holding of a palletto a support plate. With a plurality of pallets, a workpiece mounted toeach pallet, and a machining device located adjacent a lower plate in anoperating position, the workpiece-holding pallets can be connected anddisconnected to the lower plate in assembly line fashion to reducemachining time and expense.

With this set-up assembly, the center pins are spring-biased inwardlytoward the pallet. To retract the pins, the pins are pulled outwardlyagainst the spring force and then rotated perpendicularly into a latchedposition. For larger size plates, i.e., ten inches by twelve inches, thespring force is generally much higher, so that the upper plate can beheld securely in position for machining operations. Unfortunately, forupper plates of this size, the high spring force makes it difficult tomanually retract the pins outwardly from engagement.

Moreover, because of the structural relationship of the pin, the springand the lower plate, this structure does not lend itself particularlywell to automated placement, securement and removal of the upper plateto a workstation. This is due primarily to the susceptibility of pin orpin component breakage if the pin is retracted too far or rotated at thewrong time.

Also, this prior structure is not particularly suited to use with sometypes of work-holding operations. Often, the size and/or shape of thepart, or workpiece, determines the manner and the orientation in whichit should be held during a machining operation. For example, many largerparts require the use of one or more clamps, in combination with otherdevices mounted to a work table or pallet. The machining operation mayalso dictate that the part be held above a work table a predetermineddistance, or, in a sense, held in three-dimensional space.

The greater the number of mechanisms required to hold the part, the moredifficult and time consuming set up operations become. As a result ofthis increased difficulty and additional time, it also becomes moredifficult to achieve accuracy and repeatability in holding such parts,particularly odd shaped parts and/or parts which must be held above asurface to allow a machining operation to be performed. Also, for someparts, the use of clamps, which apply compression to the held part,cause distortion during the machining step. This adversely offers theaccuracy of the final machined part.

It is an objective of this invention to facilitate the automating of setup operations for accurately and repeatably holding a workpiece-holdingpallet or workpiece at a work station for the performance of a machiningoperation on the workpiece.

It is another objective of the invention to facilitate the extension andretraction of center pins used to engage a relatively large sizeworkpiece-holding pallet or workpiece at a workstation.

It is still another objective of the invention to increase versatilityin the accurate and repeatable holding of a workpiece or aworkpiece-holding pallet at a workstation, thereby to accommodatevarious sizes and shapes of workpieces and/or workpieces which must beheld above a work surface during performance of a machining operation.

This invention meets the above-stated objectives by utilizing anextendable and retractable connector which rotates into and out ofengagement with a workpiece-holding pallet, or the workpiece itself.More particularly, the connector includes a pin, an actuating knob orhandle for rotating the pin and a wrap spring which interconnects thepin and the knob in a slippable manner. The wrap spring acts as a torquelimiting device to control the pressure in one direction, and the wrapspring acts as a clutch in the opposite direction.

The pin mounts within a bore machined in a lower plate at a workstation.An external surface of the pin which is located within the bore includesa spiral cam which coacts with a radially inwardly directed cam followerthat is rigidly connected to the lower plate. The cam follower resideswithin and traverses the cam so that the pin will extend or retract uponrotation of the actuating knob. During rotation of the knob to extendthe pin, the wrap spring will slip if the knob is rotated too far. Thus,the connector acts as a torque limiting device to limit the rotationalforce applied to the pin once the pin is fully extended. Thisconstruction assures that an automatic rotating mechanism such as astepping motor will not inadvertently break the pin during extension byaccidentally rotating too far. Moreover, this construction assures that,during tightening, a predetermined bending moment will be applied to theouter support rails of the lower plate.

During rotation to retract the pin, the wrap spring acts as a clutch bymagnifying the rotational force applied to the pin. Because of thespring connection between the pin and the actuating knob, along with theslope of the spiral cam, only minimal rotational force is required torotatably retract the pin.

Preferably, four of these pins are extended into engagement with thepallet to securely hold it in place at the workstation, with the fourpins directed inwardly along a pair of spaced, parallel axes. At eachpoint of engagement, an inwardly directed end of the pin and an engagedsurface of the pallet are complementarily angled to provide precise andrepeatable positioning of the pallet for machining operations.

According to one aspect of the invention, the pallets may be machinedfrom a relatively lightweight aluminum and may be connected anddisconnected in assembly line fashion at the workstation, with each ofthe pallets holding a workpiece. Because of the spiral cam and theslippable connection between the pins and their respective actuatingknobs, this invention facilitates the automatic placement, connectionand disconnection of the pallets at a workstation with a degree ofprecision within a ten thousandth of an inch, thereby facilitatingaccurate assembly line machining of multiple workpieces mounted onmultiple pallets. The aluminum pallets may be automatically placed onthe workstation, slid laterally into position by a robot and thenaccurately secured to the workstation automatically by using steppingmotors to rotate the four pins into engagement with the pallet. Ifdesired, the sequence of operation of the robot and the stepping motionmay be controlled by a programmable computer.

Depending upon the shape and the configuration of the pallets, thisinvention also provides versatility in use. The bottom of the pallet mayinclude a pair of spaced rolls, or rounded support members, for coactingwith the pins so that the pallet may be used as a sine plate andhingedly raised at either end, as depicted and described in U.S. Pat.No. 4,927,125. Additionally, if the spaced mounting members are squaredoff on their bottoms and outer side surfaces, the pallet may actually bemounted vertically on either of its ends, perpendicular to the lowerplate. In this position, a workpiece mounted to the pallet can besupported in a desired vertical plane. In effect, this enables theworkpiece to be machined in three-dimensional space.

According to one preferred embodiment of the invention, four palletconnecting mechanisms are mounted to a lower plate which defines aworkstation. The connectors are arranged so as to engage the pallet ontwo sides, along two spaced parallel axes. For each connector, the lowerplate includes a mounting bore sized to receive a pin. The outer surfaceof the pin has a recessed spiral cam which cooperates with a radiallydirected cam follower rigidly connected to the lower plate and extendinginto the mounting bore. Upon rotation of the pin, the cam followertraverses the spiral cam and causes the pin to move axially with respectto the lower plate and to extend into or retract from engagement withthe pallet.

This spiral cam extends once around the pin and includes an initialsteeply inclined portion and a gradually inclined portion. Initially,rotation of the pin causes substantial axial movement while the camfollower traverses the steeply inclined portion of the spiral. However,after the pin has been rotated about 90°, the cam follower traverses thegradually inclined portion of the spiral, and the pin moves onlyslightly. When retracting the pin, the opposite occurs. The pininitially retracts slowly and then, in the last 90°, retractssubstantially.

The forward or inner end of each pin has an angled surface which ismachined to an angle which is complementary with an angled surface of anouter edge of a bore machined in the pallet. To connect the pallet, thepallet bores are aligned with the bores in the lower plate along thespaced axes, and the pins are extended inwardly into engagement with thepallet. The complementarily angled surfaces coact to assure that thepallet will be securely held in a precise position, within a minimaltolerance.

Each of the pins has a rearward, or outer end, which connects to anenlarged-diameter actuating knob. The knob facilitates rotation of thepin. More specifically, a wrap spring interconnects the pin and theactuating knob. The wrap spring has a radially extending tang which isheld by the actuating knob and a plurality of coils which wrap aroundthe outer surface of the pin. Depending upon which way it is desired torotate the knob to affect extension of the respective pin, and whetheror not the spring is wound with a left or right hand wrap, the tang maybe either at the forward or the rearward end of the connector. The wrapspring has an inner diameter which is slightly less than the outerdiameter of the pin, with the relative diameters depending upon theamount of torque wanted. Preferably, the inner surface of the wrapspring is flat to more securely engage the outer surface of the pin.

The wrap spring connects the actuating knob to the pin in a slippablemanner. Because of the slippable interconnection between the actuatingknob and the pin, the wrap spring acts as a torque limiting device whenextending the pin. Thus, this invention eliminates the susceptibility ofthe pin to breakage when the pin is automatically rotated to extend andretract the pin into and out of engagement with the pallet. It alsocontrols, to a preset amount, the force applied to the lower plateduring extension which may cause rail deflection. The actuating knob mayhave an outer surface which is configured to facilitate manual graspingand turning to rotate the pin. The actuating knob may also includeradially oriented holes sized to receive a radially inserted tommy barto facilitate rotation of the pin about the axis when used manually. Inan automated embodiment of the invention the actuating knob may be atoothed or beveled gear which can be easily connected to andautomatically driven by a stepping motor.

One primary advantage of this invention relates to the use of a gear anda stepping motor to rotate the pin about 360° to provide automatic,positive and precise engagement of the pin with the pallet. With foursuch pins engaging the pallet on opposite sides along a pair of spaced,parallel axes, as described above, extension and retraction of the pinsmay be fully automated with four stepping motors and a controller.

In addition to automating the extension and retraction of theconnectors, the invention contemplates the automatic placement,positioning and then removal of a pallet from a workstation using fourconnectors. According to this embodiment, each of a first pair of spacedconnectors on a first side of the workstation has a forward portion anda rearward portion, and the two portions are interconnected by aninternal compression spring aligned along the engagement axis. For eachof the first connectors, a tap screw extends internally along the outerportion, through the internal compression spring and is threaded intothe forward portion.

The spring force causes the forward portion of the pin to extendforwardly along the axis away from the rearward portion. The actuatingknob connects to the rearward portion, and the forward portion includesthe angled surface adapted to engage the side of the pallet.

With all of the connectors retracted within their respective bores, acomputer controlled robot arm places the pallet at the workstation at aposition relatively close to a predetermined machining position. Theactuating knobs of the connectors on the first side, i.e. the springloaded side, are then rotated in the direction which would normallyextend the pins. However, because the pallet blocks extension of thesepins, the internal springs compress axially as the forward portions ofthe pins bear against the side of the pallet. Thus, this rotation"loads" the internal springs.

The pallet is then moved slightly laterally to align the taperedengagement surfaces of the pallet with the four connectors. This lateralmovement allows the forward portions of the first pair of connectors toextend by spring force toward the pallet along the spaced axes and intoengagement with the pallet on the first side.

Subsequently, the actuating knobs connected to a second pair of spacedconnectors on a second, opposite side of the workstation areautomatically rotated by stepping motors to extend the second pair ofconnectors into secure engagement with the opposite side of the pallet.The force applied by the connectors on the second side also holds thepallet against the rail or shoulder at the first side of the workstation, with the same force applied each time because the force iscontrolled by the wrap springs. This method and structure connects theworkpiece holding pallet securely to the workstation in a precise andrepeatable position.

After a machining operation has been performed on the workpiece, theactuating knobs are again rotated 360° to retract all four connectorsfrom engagement with the sides of the pallet. The robot arm then picksup and removes the pallet, and another pallet is positioned at theworkstation according to the same sequence of steps. By operativelyconnecting the robot arm and the stepping motors to a programmablecontroller, this entire sequence may be automated. If desired, theworkstation may include an electronic eye, or other type of positiondetector to verify that the pallet is centered at the predeterminedposition prior to rotation of the actuating knobs to extend theconnectors into engagement with the pallet.

According to another variation of the invention, the connectors may beused to engage a workpiece itself or a workpiece-holding pallet in threedimensional space, above a work surface or work table, with theconnectors being mounted on pillars which are selectively positional onthe work table. With this variation of the invention for supporting aworkpiece or workpiece-holding pallet, a base plate or work tableincludes appropriately sized and positioned holes or recesses whichreceive the pillars.

With a plurality of such recesses, the pillars may be selectivelypositioned on the work table at locations suitable for holding aparticularly sized workpiece or workpiece-holding pallet. These recessesmay be machined in the work table to a desired shape, preferably with atleast one V-shape, with the pillars having first, or bottom, endscomplementary in shape for interfitting therein. This alternative isadvantageous for some machining operations which require a degree ofprecision such that the pillars must be secured rigidly in place. With awork table having such machined recesses, angled set screw holes must bemachined therein adjacent each recess, the set screw hole locatedopposite the V-shape. Set screws are then threaded through the holes andin to hole engagement with the pillars.

Alternatively, the recesses may actually be the standard positioning ormounting holes of a machine, such as the inverted T-slots of a standardBridgeport milling machine. If that is the case, it is preferable thento mount the pillars at the intersections of the longitudinal and thetransverse inverted T-slots.

Each pillar has a connector mounted therein, preferably orientedperpendicular to the axis of the pillar. For many workpieces orworkpiece-holding pallets, four pillars are necessary, with fourconnectors associated therewith. However, the invention alsocontemplates using three of the pillar-mounted connectors for holdingsome workpieces or pallets. At least one of the connectors should beextendable and retractable along its longitudinal axis to facilitateengaged holding and subsequent disengagement of the workpiece or palletwith extension and retraction via application of a high, or controlledpressure to actuating knobs associated therewith. This may be done byusing the wrap spring clutch described above. The other connectorsshould be spring-loaded for some extension and extraction.

The connectors may be used to suspend a workpiece of virtually any sizeor shape at a desired height above a work table, and in a desiredorientation. This is done by locating the workpiece at the desiredposition, adjacent two or more spring loaded connectors which extendfrom pillars which have been suitably positioned or secured to the worktable. At least one more, high-pressure, axially movable connector isalso located adjacent the workpiece, due to suitable securement of itsassociated pillar to the work table. By axially extending the connectorinto contact with the workpiece, the workpiece can be engaged andrigidly held in three-dimensional space. By using the wrap spring clutchdescribed above, this final holding step may be performed automatically,as by a robot, to facilitate automation of the entire workpiece holdingprocess. After machining, the connector may be retracted, automaticallyif desired, to facilitate moving the workpiece from the held position.

Because of the ease in positioning the pillars to a work table at theselected positions, and the ability to axially move at least oneconnector into and out of secure engagement with a workpiece located inthree-dimensional space, this invention simplifies set up operations forworkpieces or pallets of various size and/or shape, while also providinga high degree of accuracy and repeatable accuracy. Additionally, becauseconnectors are used, i.e. centers, this invention eliminates the needfor clamps and other holding devices that are presently used but havebeen found to generate some of the above-described problems. With theneed for such clamping devices eliminated, this invention alsoeliminates the problem of part distortion sometimes caused by performinga machining step on a part compressively held thereby.

For some workpieces, it is beneficial to keep the workpiece secured inplace on a workpiece-holding pallet during a number of sequentiallyperformed machining steps, and the pallet is moved from workstation toworkstation. In this manner, multiple pallets are used to manufacturemultiple parts, in assembly line fashion. This invention alsoaccommodates this practice because the pillars and connectors may beused to hold a workpiece-holding pallet to which the workpiece ismounted. The pillars are simply arranged on the work table in a mannerwhich accommodates the dimensions of the pallet. Since the multiplepallets each hold an identically shaped workpiece in an identicalmanner, the same high degree of accuracy and repeatability is achieved.

If a particular work table is to be used repeatedly for the sameoperation, but with workpieces or workpiece-holding pallets of differentheight, the same pillars may be used without the need for disconnectionfrom the work table. This is accomplished by mounting the connectors oncartridges of varying height, wherein the cartridges are removablyconnectable to the pillars. With a plurality of connector-equippedcartridges available for interchangeable use on the pillars, workpiecesor workpiece-holding pallets of different heights can be accommodatedwithout having to move the pillars. This is particularly advantageous ifthe connector-equipped cartridges are relatively inexpensive compared tothe pillars.

These and other features of the invention will be more readilyunderstood in view of the following detailed description and thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates, in a partial disassembled perspective, a palletwhich is connectable to a lower plate in accordance with a preferredembodiment of the invention.

FIG. 2 is a cross-sectional view taken along lines 2--2 of FIG. 1 whichdepicts a pallet constructed in accordance with a first embodiment ofthe invention.

FIG. 3 is a partial view, similar to FIG. 2, of a pallet constructed inaccordance with a second embodiment of the invention.

FIG. 4 is a partial cross-sectional view which illustrates a palletaligned with a lower plate along an axis of engagement and partiallyconnected to the lower plate via two connectors constructed according toa first preferred embodiment of the invention.

FIG. 5 is a cross-sectional view of a pallet connector in accordancewith a second preferred embodiment of the invention.

FIG. 6A is a schematic plan view of a work station in accordance withone aspect of the invention, wherein the work station is defined by alower plate which utilizes, on one side, a pair of the connectors shownin FIG. 2 and on the other side, a pair of the connectors shown in FIG.5.

FIG. 6B is a schematic plan view, similar to FIG. 6A, which depicts anupper plate or pallet after initial placement upon the lower plate, justslightly out of alignment with a predetermined machining position, andwith the connectors on the first side rotated inwardly to compressinternal springs and cause forward ends of the pins to bear against thepallet.

FIG. 6C is a partial schematic plan view, similar to FIG. 6B, whichdepicts the upper plate after it has been slid laterally on the lowerplate to the predetermined machining portion, with a spring-loadedconnector of the type shown in FIG. 5 spring-based into engagement withthe upper plate.

FIG. 6D is a partial schematic plan view, similar to FIG. 6C, whichdepicts the upper plate after the connector on the second side has beenrotatably extended into secure engagement with the pallet at thepredetermined machining position.

FIG. 7 is a perspective view of two pairs of aligned connectors mountedon upright pillars and used to suspend a workpiece in three-dimensionalspace in accordance with still another embodiment of the invention.

FIG. 8 is a schematic side view of a work system for holding awork-member in three-dimensional space, according to another variationof the invention.

FIG. 9 is a schematic plan view of the work-holding system of FIG. 8.

FIG. 10 is a perspective view which shows yet another variation of theinvention, a connector mounted to a cartridge which in turn connects toa pillar, the pillar being selectively positional on a work table.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a pallet or upper plate 10 which is used to hold aworkpiece (not shown) during a machining operation, such as grinding ormilling, etc. The pallet 10 may be formed of hard metal, aluminum orsoft steel. The pallet 10 is located above a lower plate, or mountingmember 11 which defines a workstation for performing an operation on aworkpiece (not shown) held by the pallet 10. The bottom of the pallet 10includes a pair of spaced, parallel mounting supports 14 and 15. Thesemounting supports 14 and 15 may be integrally formed with a pallet 10,or they may be removably connected thereto by screws 16 and dowel pins17, as shown in FIGS. 2 and 3.

As shown in FIG. 2, the mounting supports 14 and 15 may be round with aspecific radius if the pallet 10 is to be used as a sine plate. For workoperations which do not require the sine plate function, the mountingsupports 14 and 15 may be flat on the bottom and the outer sides, asshown in FIG. 3. This enables the pallet 10 to be connected to theworkplate 11 in either horizontal or vertical orientation, if desired.The mounting supports 14 and 15 have bores 18 and 19, respectively,machined therethrough. The outer ends of the bores 18 and 19 are taperedto define outwardly directed, angled surfaces. Bore 18 includes a pairof spaced, outwardly directed, angled surfaces 22, and bore 19 includesa pair of spaced, outwardly directed, angled surfaces 23.

The lower plate 11 includes a pair of spaced shoulders 24 and 25oriented perpendicular to the supports 14 and 15. The shoulders 24 and25 support the pallet 10 outboard of the mounting supports 14 and 15 onopposite sides of the workstation. Each of shoulders 24 and 25 has apair of spaced bores, 26 and 27, respectively, machined therethrough. Atboth ends of the lower plate 11, the bores 26 and 27 are in alignmentwith the pallet bores 18 and 19, respectively, along a pair of spacedaxes of engagement. More specifically, the bores 26 are aligned along anaxis 28 of engagement at a first end 32 of the lower plate 11.Similarly, bores 27 are aligned along an axis 29 of engagement at asecond end 33 of the lower plate 11.

Four pin assemblies, or connectors reside within the four bores 26 and27 of the lower plate 11. More specifically, two pin assemblies 34 arelocated within the two spaced bores 26 in plate 11, aligned along axis28 and directed inwardly toward each other. Similarly, two pinassemblies 35 are located within the two spaced bores 27, aligned alongaxis 29 and directed inwardly toward each other. (See FIGS. 1, 2 & 6A)

At each end 32 or 33 of the lower plate 11, the connectors 34 or 35,respectively, are mirror images of each other with respect to amid-plane parallel with shoulders 24 and 25. On each side of the lowerplate 11, the connectors 34 and 35 are mirror images of each other withrespect to a mid-plane transverse to shoulders 24 and 25.

Each pin assembly 34 or 35 includes a pin, an actuating knob or handle,and a wrap spring interconnecting the pin and the actuating knob in aslippable manner. At first end 32, each pin assembly 34 includes a pin36, an actuating knob 38 and a wrap spring 40. Similarly, at second end33, each pin assembly 35 includes a pin 37, an actuating knob 39 and awrap spring 41. Each pin 36 or 37 has a preferable length of about2.568", an outer diameter of about 0.500" at its forward or inner endand an outer diameter of about 0.565" at its outer or rearward end.

Applicant has used wrap springs 40 and 41 made of round, spring steelwire having a diameter of about 0.148". The wrap springs 40 and 41 weremade from a coil with about 41/3 or more turns, the coil having aninitial outer diameter of about 0.843" and an initial inner diameter ofabout 0.547". The inner diameter and outer diameter of the coil werethen ground to dimensions of 0.552" and 0.824", respectively. Thisproduced wrap springs 40 and 41 with a flat inside surface, therebyincreasing the clutching or grabbing power. With these dimensions, whenthe connector 34 or 35 is rotatably extended into engagement with thepallet 10, the wrap spring 40 or 41 should slip upon application of 30inch pounds of torque about the axis 28 or 29, respectively.

For optimum results, it is believed that the wrap springs 40 and 41should be made from a wire which is rectangular in cross section. Thisrectangular shape would minimize any adverse affects on the springcharacteristics caused by grinding the inner and outer diameters afterheat treatment.

Each pin 36 or 37 includes an angled or tapered surface 44 or 45,respectively, at its forward or inner end which engages the pallet 10.Preferably, these surfaces 44 and 45 are tapered at an angle of about7°30' around the entire circumference of the respective pin 36 or 37.The surfaces 44 and 45 engage the complementarily angled surfaces 22 and23, respectively, at the outer ends of the bores 18 and 19. Thecomplementary angles coact to hold the pallet 10 in a precise andrepeatable position at the workstation, as shown in FIG. 4.

Each pin 36 or 37 has a spiral cam 50 or 51, respectively, formed in itsouter surface. FIG. 4 shows two cams 50 in the outer surfaces of twospaced pins 36. The cams 50 coact with cam followers 52 which areconnected to the lower plate 11 and which extend radially into the bores26. Preferably, the cam followers 52 are hardened and ground 0.1875"pins. The cam followers 52 slide into the outer side of the lower plate11 at first end 32 and extend radially into the bores 26. The camfollowers 52 are retained with a small amount of clearance with a smallbutton head Allen screw threaded into lower plate 11 at first end 32.The head of screw 52a holds in place the radial outer end of the camfollower 52. Preferably, each cam follower 52 is internally threaded atits outer end so that it can be removed. During rotation of the pins 36to extend and retract the connectors 34 into and out of engagement withthe pallet 10, the cam followers 52 traverse the cams 50. Similarly, atthe second end 33, the two pins 37 include cams 51 which coact with camfollowers 53, and cam followers 53 are held in place by screws 53a.

Preferably, each cam 50 or 51 extends about 360° around the respectivepin 36 or 37, and includes a steeply inclined portion 54 or 55 and agradually inclined portion 56 or 57 (FIG. 1). The gradually inclinedportion 56 or 57 extends about 270° around the respective pin 36 or 37.The steeply inclined portion 54 or 55 extends about 90° around therespective pin 36 or 37. The cams 50 or 51 are located about midwaybetween the forward and rearward ends of the respective pins 36 or 37.

For each connector 34 or 35, rotating inwardly about the respective axis28 or 29 ("inward" rotation is shown by directional arrows 58 and 59 inFIG. 1) extends the respective pin 36 or 37 toward the pallet 10. Duringinitial rotation, and for about 90° of rotation, the cam followers 52 or53 traverse the steeply inclined portions of the respective cams 50 or51, thereby substantially extending the respective pins 36 or 37. Duringrotation through the steep portions, each of the pins 36 or 37 of theconnectors 34 or 35 extends toward the pallet 10 along the respectiveaxis 28 or 29 a distance of about 0.125". During rotation through thegradually inclined portion 56 or 57, each pin 36 or 37 extends aboutanother 0.027", thus, the total horizontal travel of each pin 36 or 37is about 0.152".

These dimensions may vary due to heat treatment. Moreover, if theconnectors on one side have greater holding force then the connectors onthe opposite side, as was described in the previously identified patentand later in this detailed description, the horizontal travel will ceaseafter the pin 36 or 37 has contacted the member 14 or 15 and pushed theupper plate 10 against the opposite rail 24 or 25.

At its rearward or outer end, each connector 34 or 35 includes a pair ofspaced washers 60 and 62, or 61 and 63, located on opposite sides of therespective wrap spring 40 or 41 and which enclose the axial ends of therespective actuating knob 38 or 39. As shown in FIG. 4, each connector34 includes an inner washer 60 and an outer washer 62. Likewise, eachconnector 35 includes an inner washer 61 and an outer washer 63.Preferably, each pin 36 or 37 also includes a circumferential groove cutinto its outer surface, just inward of the respective inner washer 60 or61. This groove receives a snap ring 64 or 65 for holding the respectiveinner washer 60 or 61 in place. More specifically, as shown in FIG. 4,each of the snap rings 64 holds in place an inner washer 60. Finally,each pin 36 or 37 has a hollowed outer end which is internally threadedto receive an axially directed screw 66 or 67 to hold the parts of therespective connector 34 or 35 together.

For connector 34, at its outer end, the wrap spring 40 includes aradially outwardly directed tang 72 which is received within a radiallydirected recess 74 in actuating knob 38, and similarly for connector 35,at its outer end, the wrap spring 41 includes a radially outwardlydirected tang (not shown) which is received in a radially directedrecess (not shown) in actuating knob 39. The wrap springs 40 or 41 arecoiled such that, when the respective pins 36 or 37 are rotatablyextended, the frictional engagement between the inner surfaces of thewrap springs 40 or 41 and the outer surfaces of the pins 36 or 37couples the rotational movement of the actuating knobs 38 or 39 to therespective pins 36 or 37.

For one 360° rotation, the rotational force applied to the knob 38 or 39is directly coupled to the respective pin 36 or 37. After the knob 38 or39 has been rotated 360° and the cam follower 52 or 53 has traversed therespective cam 50 or 51, any additional rotational force or torqueapplied to the knob 36 or 37 will cause the respective wrap spring 40 or41 to slip around the pin 36 or 37. The slip torque for each connector34 or 35 depends upon the relative diameters and the shapes of the wrapspring 40 or 41 and the pin 36 or 37. The relative diameters of the wrapspring 40 or 41 and the respective pin 36 or 37 may be varied as desiredto provide a pre-set maximum applicable torque to the respective pins 36or 37 after rotatable extension into engagement with the pallet 10. Byusing a slippable connection to limit the amount of torque that may beapplied to the pins 36 and 37 upon rotation of the respective actuatingknobs 38 and 39, the susceptibility of the pins 36 and 37 to breakagedue to inadvertent over rotation is eliminated. Moreover, because of theconfiguration of the spiral cam 50 or 51, i.e. the steeply inclinedportion 54 or 55 and the gradually inclined portion 56 or 57, theinitial 90° of rotation of the actuating knob 38 or 39 causes engagementwith the pallet 10, and then the subsequent 270° of rotation causessmooth alignment and centering of the pallet bores 18 and 19 with thepins 36 and 37.

To rotatably retract the pins 36 or 37, the respective actuating knobs38 or 39 are rotated outwardly in directions opposite from thedirections shown by directional arrows 58 and 59, on both sides of thelower plate 11. During rotation of the actuating knobs 38 or 39 toretract the pins 36 or 37, the cooperative interaction of the tangs 72or 73 held by the radial recesses 74 or 75 of the respective actuatingknobs 38 or 39 tightens the holding force or grip of the wrap springs 40or 41 upon the respective pins 36 or 37. As a result, the wrap springs40 or 41 act as clutches to couple and magnify the rotational forceapplied to the pins 36 or 37 by rotation of the respective knobs 38 or39. Because initial rotation to retract the pin 36 or 37 occurs whilethe cam follower 52 or 53 traverses the gradually inclined portion 56 or57 of the respective cam 50 or 51, and because the wrap spring 40 or 41serves as a clutch between the actuating knob 38 or 39 and the pin 36 or37, it is relatively easily to manually rotate the actuating knob 38 or39 to retract the respective pin 36 or 37 out of engagement with thepallet 10.

To facilitate rotation for both extension and retraction of the pins 36or 37, the actuating knobs 38 or 39 preferably include outer surfaceswhich are easy to grasp and rotate manually. More particularly, eachactuating knob 38 preferably includes a plurality of smooth surfaces 78spaced on centers around the axis 28. As shown in FIG. 1, actuating knob38 includes four smooth surfaces 78 located on 90° centers. Betweenevery two smooth surfaces 78, each actuating knob 38 also includes aradially oriented aperture 80. Thus, actuating knob 38 also includesfour apertures 80 spaced on 90° centers about axis 28. Similarly, eachactuating knob 39 includes four apertures 81 spaced on 90° centers aboutaxis 29 and located between four smooth surfaces 79 which are alsospaced on 90° centers. The apertures 80 and 81 are sized to receiveradially inserted "tommy" bars to facilitate rotation of the actuatingknobs 38 or 39 about the respective axis 28 or 29.

FIG. 1 through 4 show the details of this invention with respect to anupper plate 10 adapted to be received on and secured to lower plate 11,wherein the connectors 34 and 35 are mounted to the lower plate 11. Thisarrangement is preferable if the number of work stations is relativelylow compared to the number of parts which will be machined.

However, it is also to be understood that the invention contemplates theproviding of supports 14 and 15 mounted to lower plate 11, with theshoulders 24 and 25 mounted to upper plate 10, so that the connecters 34and 35 are carried by the upper plate 10. In effect, this arrangementwould be an upside down version of what is shown in the Figures. Thisupside down version would be preferable if the number of workstationswere relatively large in comparison to the number of parts machined.

For either of these two arrangements, with the members 14 and 15rounded, the plate 10 and plate 11 are hingeably moveable about eitherof the two spaced axes 28 and 29. Moreover, if the members 14 and 15 aresquared off on their bottom and outer sides, either of these twoarrangements enables the upper plate 10 to be oriented perpendicular tothe lower plate 11.

For use as a pallet changing system, it is preferable to mount theconnectors 34 and 35 to the lower plate 11 so that the upper plate 10can be made as light as possible, thereby minimizing the amount ofweight that must be lifted. The embodiment of the invention described inFIG. 1 works particularly well as a sine plate or as a pallet systemwherein the upper plate 10 is manually placed upon and secured to thework station defined by the lower plate 11.

The described embodiment is also particularly suitable for automatedextension and retraction of the connectors 34 and 35 into engagementwith the pallet 10. The slippable interconnection between the pins 36 or37 and the respective actuating knobs 38 or 39 allows extension orretraction to be performed automatically, as by a stepping motor. Forautomatic extension and retraction, the actuating knobs 38 and 39 arepreferably replaced with toothed gears.

Additionally, this invention further contemplates fully automating thesequential placement, securement and removal of a plurality of pallets10 to the work station 11 in assembly line fashion. To fully automatethis process, the invention contemplates the use of a connector or pinassembly 82 which is depicted in FIG. 5. The connector 82 is similar toconnector 34 in many respects.

However, connector 82 also includes an internal compression spring 84which resides within a spring pocket 86 and forces a first portion 88 ofpin 36 from a second portion 90 thereof along the axis 28. The pin 36has an internal bore 92 along its axial length. Preferably, the bore 92has a reduced diameter forward portion 94 with a diameter of about0.150", and an enlarged diameter rearward portion 96 with a diameter ofabout 0.257". The bore 92 receives an internal tap screw 98 whichextends forwardly through spring 84 and threads within the first portion88. The rearward portion 96 of bore 92 is oversized with respect to thescrew 98 to permit rotational movement therebetween. The screw 98maintains a maximum spacing of 0.130" between the first portion 88 andthe second portion 90.

The connector 82 also has a spiral cam 50, but it is not necessary forthe cam 50 to have a gradually inclined section and a steep section. Theconnector 82 is utilized in an embodiment of the invention which isdepicted sequentially in FIG. 6A, 6B, 6C and 6D. As shown in FIG. 6A,the connector 82 is aligned along axis 28 at the first end 32 of thework station 11. Another connector 83 is the mirror image of connector82 with respect to a midplane transverse to shoulders 24 and 25. Theconnector 83 is aligned along the axis 29 at the second end 33 of workstation 11.

Preferably, as shown in FIG. 6A, the actuating knobs 38 and 39 ofrespective connectors 82 and 83 are shown as toothed gears to facilitatecoupling with a toothed gear (not shown) mounted to a shaft (not shown)of a first stepping motor 100a. Alternatively, the actuating knobs 38and 39 may be connected to the motor 100a by a belt or by a beveled gear(represented by dash lines), so long as the connectors 82 and 83 may beautomatically extended and retracted by rotating 360° about axes 28 and29, respectively.

Similarly, on an opposite side of the work station 11, connectors 34 and35 are aligned along axis 28 and axis 29, respectively. The connectors34 and 35 are similar to the connectors described previously withrespect to FIG. 1-4. However, the actuating knobs 38 and 39 ofrespective connectors 34 and 35 are also shown as toothed gearsoperatively connected to a second stepping motor 100b.

Initially, all of the connectors 82 and 34 and 83 and 35 are retractedwithin their respective bores 26 and 27, respectively, in the workstation 11. In this position, the work station 11 is ready forplacement, transfer, sliding, securement and then removal of pallet 10by a robot arm (not shown).

The pallet 10 is then placed upon work station 11 automatically, as by arobot arm (not shown). As shown in FIG. 6B, the pallet 10 is placed onthe work station 11 in a position slightly offset laterally with respectto the final desired machining position.

Thereafter, motor 100a rotates connectors 82 and 83 in the direction ofarrows 58 and 59, respectively. This moves actuating gears 38 and 39,respectively, closer to shoulder 24. However, because the offsetlocation of the pallet 10 blocks extension of the connectors 82 and 83,the respective forward portions 88 and 89 bear against the pallet 10 andare thus not able to extend beyond shoulder 24. As a result, the springs84 and 85 are axially compressed. Thus, this step "loads" the internalsprings 84 and 85.

With the upper plate 10 supported on the work station 11, the robot arm(not shown) applies a horizontal force in the direction shown bydirectional arrow 102 to laterally slide the pallet 10 along the workstation 11. Eventually, bores 18 and 19 in members 14 and 15,respectively, will come into alignment with the bores 26 and 27. Whenthis occurs, the springs 84 and 85 will cause the first portions 88 and89, respectively, to extend into initial engagement with bores 18 and 19on the first side of the work station 11. This temporarily holds thepallet 10 at the desired machining position. FIG. 6C shows the secondend 33 of the work station 11 after spring extension.

Subsequently, motor 100b rotates actuating gears 38 to 39 to rotatablyextend the connectors 34 and 35, respectively, into engagement with thepallet 10 on the second side of the workstation 11. This rotation ofconnectors 34 and 35 holds the pallet 10 in dead center position withrespect to axes 28 and 29. Moreover, the force applied via connectors 34and 35 when in their extended positions holds the pallet 10 securelyagainst the shoulder 24 on the first side of the work station 11,thereby providing for accurate positioning and machining of a work-pieceheld on the pallet 10. FIG. 6D shows the connectors 83 and 35 inengagement with the pallet 10 adjacent the second end 33 of the workstation 11.

After a machining operation is completed, the connectors 82, 83, 34 and35 are rotatably retracted from engagement with the pallet 10, and thepallet 10 is picked up by a robot arm (not shown) and moved to anotherstation 11. Thereafter, another identical pallet 10 holding a workpieceis placed upon the work station 11.

Preferably, the stepping motors 100a and 100b and the robot arm (notshown) are operatively connected to a master, programmable controller(not shown) so that this entire operation can be performed according toa desired sequence and duration of steps. If desired, in addition to, oras an alternative to the use of spring-loaded connectors 82 and 83, thework station 11 may include one or more position sensors connected tothe controller to indicate when pallet 10 has been placed upon workstation 11 and/or laterally slid into the desired machining position onthe work station 11.

As yet another embodiment, this invention further contemplates the useof a plurality of connectors 34 or 35 to actually hold the workpieceitself, without mounting the workpiece to a pallet 10. According to thisembodiment of the invention, as shown in FIG. 7, a work station 11 orwork table is defined by two stacked plates 124 and 125. The bottomplate 124 may be smooth on its top surface, or similar to other standardwork tables, while top plate 125 has a plurality of shaped recesses 126machined in an exposed surface thereof, with each recess 126 having oneV-shaped corner. Each recess 126 is adapted to receive a complementaryshaped bottom end of a pillar 128 of predetermined height. Preferably,the pillar 128 is held against the V-shaped corner of the recess 126 bya screw threaded into on angled screw hole 127 located adjacent a flator angled side of the recess 126. A plurality of pillars 128 ofdifferent height may be provided. Each pillar 128 includes a horizontalbore for receiving and horizontally supporting a connector 34. Each ofthe connectors 34 is rotatably extendable and retractable along itsaxis, preferably in a horizontal plane determined by the height of therespective pillar 128.

If desired, the top plate 125 itself may serve as the work table, withrecesses of the type shown in FIG. 7 formed therein, or otherstandardized recesses such as the inverted T-shape of a Bridgeportmachine.

With a workpiece of a particular shape and configuration located at awork location within four pillars 128, and with the respectiveconnectors 34 aligned with, or directed toward rigid and engageablesurfaces of the workpiece, extension of at least one of these alignedconnectors 34 into engagement with the workpiece causes all of theconnectors to engage the workpiece, thereby holding the workpiecesecurely in a predetermined position for the performance of a machiningor manufacturing operation.

FIGS. 8 and 9 show another variation of the invention, a work-holdingsystem for holding a work member 110, which may be a workpiece or aworkpiece-holding pallet, in three-dimensional space above a work table125. This facilitates access for certain machining operations andeliminates the need for distortion-causing clamps. The work member 110is held by a plurality of connectors 144, in this case three, at leastone of which is extendable or retractable about its axis with the use ofhigh or controlled pressure, as by the wrap-spring structure describedabove, and the others of which are spring loaded. Preferably, the atleast one high pressure connectors 144 has an actuating knob 134aassociated therewith which facilitates automatic extension andretraction, such as a gear. The connectors 144 mount to pillars 128which are selectively positionable and securable to the work table 125at desired positions, via interaction with recesses 125, which in FIGS.8 and 9 are inverted T-slots. With the embodiment of FIGS. 8 and 9, eachpillar 128 has a corresponding mounting support 128a shapedcomplementary to the recess 126, and the mounting support 128a ispreferably threadably tightenable to the table 125, as is common in theindustry for mounting workpiece fixtures to work tables having invertedT-channels. This holds the pillar 128 securely to the table 125.

With the connectors 144 directed toward a work holding location,preferably directed inwardly, the work member 110 may be positionedtherewithin. By actuating, i.e. rotating, the actuating knobs 134a, theconnector 144 associated therewith extends inwardly to engage the workmember 110, to hold it securely at the work-holding location. Amachining operation may then be performed, and the connector 144 maythen be retracted to disengage the work member 110 for movement toanother work station, and the same process then repeated on the nextwork member 110. The invention facilitates automation of theseoperations, due to the ease in operation of the wrap spring clutch.Moreover, the selective positioning of the pillars 128 significantlyreduces the time and costs associated with set up of operations.

FIG. 10 shows another variation of this embodiment of the invention. Thepillar 128 itself does not have a connector 144 mounted directlythereto. Rather, for each pillar 128, the connector 144 and theactuating knob 134 associated therewith is mounted to a cartridge 150which is removably connectable to the pillar 128, as by a bolt 151. Thebolt 151 may also serve in a dual role for tightening the mountingsupport 128a. Additionally, removable keyways may be used on two or moresides to connect the cartridges 150 to the pillars 128, to preventrelative axial movement therebetween. This enables the pillars 128 toremain secured to the table 125 at particular positions which are usedregularly, but which require the connectors 144 to be at differentvertical levels, due to the size, shape and/or machining operation to beperformed on a workpiece.

If desired, the pillars 128 may extend horizontally from a plate 125which is oriented vertically, or the plate 125 oriented at any otherdesired angle, with the pillars 128 preferably extending perpendicularlytherefrom, but not necessarily.

This embodiment of the invention may be used to temporarily hold avariety of differently sized and shaped objects in a rigid position,from an engine block to a toaster. The invention may also be used inother diverse work environments, such as medicine. For instance, atleast three of the connectors may be used to hold a patient's headduring surgery, with two being spring loaded connectors and one being acontrolled pressure connector. The controlled pressure connector may beextended to cause engagement and securement of the head by all threeconnectors. Preferably, for this use, the connectors are equipped withtooling balls at their inner ends, and these tooling balls are receivedwithin angled or curved female connectors screwed into the patient'sskull. The female connectors may be initially located for placement witha ring, which is then used to correlate the pillar positions.

In another variation of the embodiment shown in FIG. 7, each recess 126may be used to hold a relatively small size workpiece, with theworkpiece held against the V-shaped corner by an opposing screw hole127.

In addition to use in holding a workpiece-holding pallet, a sine plateor a workpiece, these connectors 34 could be incorporated into thedesign of an article of manufacture to render the article easy toassemble or disassemble, a feature that would be particularlyadvantageous in designing and manufacturing articles wherein thecomponents must be recyclable.

While these and other features of a pallet/sine plate connector and awork-holding system in accordance with several preferred embodiments ofthe invention have been described, including several variations thereof,it is to be understood that the invention is not limited thereby and inlight of the present disclosure, various other alternative embodimentswill be apparent to one of ordinary skill in the art without departingfrom the scope of the invention. Accordingly, applicant intends to bebound only by the following claims.

I claim:
 1. A work-holding system for rigidly holding a work memberduring a work operation comprising:a work table having a plurality ofrecesses formed in an exposed surface thereof; a plurality of pillars,each pillar having a first end sized to be received within one of therecesses, the pillars being selectively positionable to the work tableat desired locations to define a workholding location therewithin; and aplurality of connectors, each connector being secured to a respectivepillar and extending toward the work-holding location, a first connectorbeing further extendable and retractable with respect to a first pillarassociated therewith, in directions toward and away from thework-holding location, respectively, whereby a plurality of connectorsmounted to a like number of pillars are adapted to engagably hold a workmember at the work-holding location by extension of the first connectorinto engagement with the work member at the work-holding location, thefirst connector spirally engaging the first pillar and thereby beingextendable and retractable toward and away from the work-holdinglocation by rotation with respect to the first pillar, the firstconnector further including a pin, an actuating knob and a wrap springoperatively interconnecting the pin and the actuating knob in aslippable manner, the wrap spring serving as a torque limiting deviceduring rotation of the knob with respect to the pillar in a firstdirection, thereby to extend the pin toward the work-holding location,and serving as a clutch during rotation of the knob with respect to thepillar in a second direction, thereby to retract the pin from thework-holding location.
 2. The work-holding system of claim 1 wherein thework table is oriented horizontally, the pillars are oriented verticallyand the connectors are oriented horizontally.
 3. The work-holding systemof claim 1 wherein the work member comprises a workpiece.
 4. Thework-holding system of claim 1 wherein the work member comprises aworkpiece-holding pallet.
 5. The work-holding system of claim 1 andfurther comprising:a plurality of cartridges, each cartridge removablymountable to one of the pillars, the connectors mounted to thecartridges.